The invention relates to a mixture of a novel type of liquid crystals in the form of triphenylene derivatives which are sensitive to the electrical field and therefore usable in electrooptical devices. They are called disc-like or discotic liquid crystals.
It is known that the hitherto used liquid crystals are nematic or cholesteric liquid crystals on the one hand and smectic liquid crystals on the other. These products are formed from long or rod-like molecules.
The constitution of electrooptical cells is also known and they use nematic, smectic or cholesteric rod-like molecules and a survey thereof is given, for example, in articles such as "Etudes sur les applications a la visualisation des cristaux liquides, les tendances" (Studies of the tendencies in the uses of liquid crystals for visual display purposes) by M. HARENG and S. LE BERRE, Annales de Physique, 1978, Vol.3, p.317or "Electrooptical applications of liquid crystals" by J. D. MARGERUM et al in the Journal of Colloid and Interface Science, Vol.58, No.3, March 1977.
Recently, liquid crystals differing from rod-like liquid crystals have been discovered, cf for example the article "Une mesophase disquotique" (A disc-like mesophase) by J. Billard, JC DUBOIS, Nguyen Huu TINH and A. ZANN in Nouveau Journal de Chimie, Vol.2, No.5, p.535, 1978. These liquid crystals are formed from disc-like molecules present in the carbon-containing mesophases, but which had not previously been isolated. A disc-like polymorphism exists, so that there are several types of disc-like mesophases.
It has been found in the laboratories of the Applicant company that by mixing certain triphenylene derivatives low temperature liquid crystals are obtained having a so-called "thread" disc-like mesophase sensitive to the electrical field. The "thread" disc-like mesophase is also called "highly fluid meosphase," "fluid mesophase" or "nematic disc-like mesophase," these latter terms being used in Nguyen Huu Tinh et al., Physics Letters, Vol. 72 A, No. 3, pages 251-254 (1979).